Coverless Steganography Based on Motion Analysis of Video

Algorithm 3

Information extraction.

	Input: video database , smoothing window size for optical flow calculation W, number of LK pyramid level L, bin number N, mapped index set , and number of index items m
	Output: secret information bitstream
(1)	For i = 1 : m
(2)	Get video ID, frame ID, and subblock ID from the index item i
(3)	P = VideoToFrame (Vvideo ID)
(4)	Convert RGB to gray: R1 = Rgb2gray (PFrame_ID), R2 = Rgb2gray (PFrame_ID +1),
(5)	Median filtering: M1 = medfilt (R1), M2 = medfilt (R2)
(6)	Calculate the hierarchical optical flow matrixes between corresponding frames: (u, ) = HierarchicalLK (M1, M2, W, L)
(7)	Calculate the gradient histogram of optical flow of the corresponding subblock: HSubblock_ID = gradientHist (u, , N)
(8)	Hsi = HashCalc (HSubblock_ID)
(10)	End for
(11)	Connect all the segments as {Hs1, Hs2, …, Hsm}
(12)	Remove padding bits, and the secret information bitstream is recovered: